U.S. patent application number 14/118025 was filed with the patent office on 2014-08-14 for method of cooling a torrefied material.
The applicant listed for this patent is Katarina berg, Anders Nordin, Martin Nordwaeger, Ingemar Olofsson, Linda Pommer. Invention is credited to Katarina berg, Anders Nordin, Martin Nordwaeger, Ingemar Olofsson, Linda Pommer.
Application Number | 20140223810 14/118025 |
Document ID | / |
Family ID | 47177198 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140223810 |
Kind Code |
A1 |
Nordin; Anders ; et
al. |
August 14, 2014 |
Method of Cooling a Torrefied Material
Abstract
The invention relates to a method and a system for efficient
cooling of torrefied material which also increases energy yield and
hydrophobicity of the torrefied product and decreases clogging of
the cooling device. The method includes that at least a part of
cooled torrefied material is mixed-back with hot torrefied material
before the hot material is introduced into a cooling device for
further cooling of the torrefied material.
Inventors: |
Nordin; Anders; (Umea,
SE) ; Pommer; Linda; (Umea, SE) ; berg;
Katarina; (Nordmaling, SE) ; Olofsson; Ingemar;
(Umea, SE) ; Nordwaeger; Martin; (Umea,
SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nordin; Anders
Pommer; Linda
berg; Katarina
Olofsson; Ingemar
Nordwaeger; Martin |
Umea
Umea
Nordmaling
Umea
Umea |
|
SE
SE
SE
SE
SE |
|
|
Family ID: |
47177198 |
Appl. No.: |
14/118025 |
Filed: |
May 16, 2012 |
PCT Filed: |
May 16, 2012 |
PCT NO: |
PCT/SE2012/050526 |
371 Date: |
February 3, 2014 |
Current U.S.
Class: |
44/589 ; 44/635;
44/636 |
Current CPC
Class: |
Y02E 50/10 20130101;
C10L 5/447 20130101; C10B 53/02 20130101; Y02E 50/14 20130101; C10B
57/02 20130101; Y02E 50/30 20130101; C10L 9/083 20130101; Y02E
50/15 20130101; C10B 7/10 20130101 |
Class at
Publication: |
44/589 ; 44/635;
44/636 |
International
Class: |
C10L 5/44 20060101
C10L005/44 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2011 |
SE |
1150467-8 |
Claims
1. A torrefaction method, comprising the steps of: a) subjecting an
optionally pretreated biomass to torrefaction to produce a
torrefied material and torrefaction gases; b) cooling and
optionally compacting the torrefied material from step a); c)
mixing at least part of the material from step b) with at least
part of the torrefaction gases and/or torrefied material from step
a) such that torrefaction gas components condense on the material
from step b).
2. The method according to claim 1, wherein step b) comprises
transportation of the torrefied material through a cooled drum by
means of a screw.
3. The method according to claim 1, wherein the temperature of the
material from step b) is less than 100.degree. C.
4. The method according to claim 1, wherein the torrefied material
is compacted in step b) and mixed with the torrefied material from
step a) in step c) and then separated from the torrefied
material.
5. The method according to claim 4, wherein the compacted material
is separated by means of a sieve.
6. The method according to claim 1, wherein the biomass is dried
and optionally heated prior to step a) to generate gases which are
not mixed with the torrefaction gases before or in step b).
7. A torrefaction system, comprising: a torrefaction reactor for
converting an optionally pretreated biomass to a torrefied material
and torrefaction gases; an arrangement comprising means for cooling
and optionally compacting the torrefied material, said arrangement
comprising an inlet connected to an outlet of the torrefaction
reactor; a mixing zone for mixing the torrefaction gases and/or
torrefied material from the torrefaction reactor with material from
the arrangement such that torrefaction gas components may condense
on the material from said arrangement, wherein the mixing zone is
connected to an outlet of the arrangement via means for material
transport.
8. A torrefaction system according to claim 7, wherein the mixing
zone is arranged in the connection between the outlet of the
torrefaction reactor and the inlet of the arrangement.
9. A torrefaction system according to claim 7, wherein the
arrangement comprises means for compacting the torrefied material,
the system further comprising a device for separating compacted
torrefied material from non-compacted torrefied material.
10. A torrefaction system according to claim 9, wherein the
separating device is arranged in the arrangement upstream of the
means for compacting the torrefied material.
11. A torrefaction system according to claim 8 wherein the
separating device is a sieve.
Description
TECHNICAL FIELD
[0001] The present invention relates to the field of torrefaction
of biomass. In particular, it relates to a method and a system for
efficient cooling of torrefied material which also increases energy
yield and hydrophobicity of the torrefied product and decreases
clogging of the cooling device.
BACKGROUND
[0002] To be able to compete with and replace fossil fuel energy
carriers such as coal, oil and natural gas, lignocellulosic biomass
would benefit from some form of pre-treatment method to overcome
inherent drawbacks. The pre-treatment method torrefaction has been
shown to improve biomass fuel qualities such as energy density,
water content and milling, feeding and hydrophobic properties
[1-4]. These improvements establish torrefaction as a key process
in facilitating an expanding market for biomass raw materials.
Torrefaction is a thermal pre-treatment method that normally takes
place in a substantially inert (oxygen free) atmosphere at a
temperature of about 220-600.degree. C. During the process course a
combustible gas comprising different organic compounds is produced
from the biomass feedstock in addition to the torrefied
biomass.
[0003] The process of producing a torrefied material from
lignocellulosic biomass can be said to include four stages:
1) a drying step, wherein free water retained in the biomass is
removed; 2) a heating step in which physically bound water is
released and the temperature of the material is elevated to the
desired torrefaction temperature; 3) a torrefaction stage, in which
the material is actually torrified and which starts when the
material temperature reaches about 220.degree. C.-230.degree. C.
During this stage, the biomass partly decomposes and gives off
different types of volatiles, such as hydroxy acetone, methanol,
propanal, short carboxylic acids etc. In particular, the
torrefaction stage is characterized by decomposition of
hemicellulose at temperatures from 220.degree. C.-230.degree. C.,
and at higher torrefaction temperatures cellulose and lignin also
starts to decompose and give off volatiles; cellulose decomposes at
a temperature of 305-375.degree. C. and lignin gradually decomposes
over a temperature range of 250-500.degree. C.; 4) a cooling step
to terminate the process and facilitate handling. The torrefaction
process is terminated as soon as the material is cooled below
220.degree. C.-230.degree. C.
SUMMARY OF THE PRESENT DISCLOSURE
[0004] During the cooling process of torrefied material, the
material continues to release gases until the temperature of the
material is decreased below about 200.degree. C. However, the
material need to be further cooled to below 130.degree. C. to
ensure safe self ignition temperatures. Therefore, in the prior
art, torrefied material have been directly cooled in a cooling
device such as a screw cooler to decrease the temperature to below
130.degree. C., see e.g. WO2009/151367 A1. One problem with this
approach is that the gases given off from the torrefied material
during the cooling process will condense on cold surfaces within
the cooling device leading to fouling or clogging of said device.
Another problem with the cooling processes of torrefied material
described in the prior art is that the gases given of during the
cooling process leads to a decrease in energy yield of the
torrefied product. There is thus a demand for an improved method
for cooling torrefied material.
[0005] The present inventors have solved the problems described
above by a method for cooling torrefied material. Said method
includes that at least a part of cooled torrefied material is
mixed-back with hot torrefied material before the hot material is
introduced into a cooling device for further cooling of the
torrefied material. This method has several advantages compared to
the methods described in the prior art: [0006] 1) Gases given off
by the hot material within the cooling device, and torrefaction
gases introduced into the cooling device, will condense on the cold
torrefied material which will decrease condensation on cold
surfaces within the cooling device which in turns decrease clogging
of said cooling device. [0007] 2) Condensation of gases on the
torrefied material in the mixing step or in the cooling device,
increases the energy yield of the final torrefied product, [0008]
3) Condensation of gases on the torrefied material in the mixing
step or in the cooling device increases the hydrophobicity of the
final torrefied product, which often is a highly desired
characteristic of the torrefied products.
[0009] Accordingly the present invention relates to a torrefaction
method, comprising the steps of:
a) subjecting an optionally pretreated biomass to torrefaction to
produce a torrefied material and torrefaction gases; b) cooling and
optionally pelletizing the torrefied material from step a); c)
mixing at least part of the material from step b) with at least
part of the torrefaction gases and/or torrefied material from step
a) such that torrefaction gas components condense on the material
from step b).
[0010] Another aspect of the invention relates to a torrefaction
system, comprising:
[0011] a torrefaction reactor for converting an optionally
pretreated biomass to a torrefied material and torrefaction
gases;
[0012] an arrangement comprising means for cooling and optionally
pelletizing the torrefied material, said arrangement comprising an
inlet connected to an outlet of the torrefaction reactor;
[0013] a mixing zone for mixing the torrefaction gases and/or
torrefied material from the torrefaction reactor with material from
said arrangement such that torrefaction gas components may condense
on the material from said arrangement, wherein the mixing zone is
connected to an outlet of said arrangement via means for material
transport.
BRIEF DESCRIPTION OF THE FIGURES
[0014] FIG. 1 shows a torrefaction system comprising a torrefaction
reactor, connected to an arrangement for cooling torrefied
material.
[0015] FIGS. 2a and 2b show two different torrefaction
reactors.
[0016] FIGS. 3 and 4 show time and temperature of a biomass in a
torrefaction reactor connected to an arrangement for cooling
torrefied material. The arrows indicate quench cooling with cold
torrefied material.
DEFINITIONS
Torrefaction:
[0017] A thermal pre-treatment method that takes place in a
virtually inert (oxygen-reduced or oxygen free) atmosphere at a
temperature above 220.degree. C. but below 600.degree. C. and which
produces a torrefied biomass and combustional gases. During a
torrefaction stage, parts of the biomass, in particular
hemicellulose, decompose and give off different types of organic
volatiles. In a torrefaction process starting from raw biomass, the
actual torrefaction stage is preceded by a drying stage wherein
free water retained in the biomass is removed and by a heating
stage wherein the biomass is heated to the desired torrefaction
temperature.
Heating Zone:
[0018] A specific region of a compartment in a torrefaction
reactor, located upstream of a torrefaction zone in relation to a
biomass inlet of a torrefaction reactor, comprising means for
specifically regulating the temperature in said specific region and
wherein the temperature of a biomass is increased to a temperature
near the desired torrefaction temperature prior to
torrefaction.
Torrefaction Zone:
[0019] A specific region of a compartment in a torrefaction
reactor, located downstream of a heating zone in relation to a
biomass inlet of a torrefaction reactor, comprising means for
specifically regulating the temperature in said specific region and
wherein the temperature of a previously heated biomass is kept
virtually constant at the desired torrefaction temperature for a
desired torrefaction time wherein a desired torrefaction
temperature is in a range between 220.degree. C. to 600.degree.
C.
Drying Zone
[0020] A specific region of a compartment in a torrefaction
reactor, located upstream of a heating zone in relation to a
biomass inlet of a torrefaction reactor, comprising means for
regulating the temperature in said specific region and wherein a
biomass is dried to a water content below 10% prior to heating.
Connecting Zone
[0021] A specific region in a torrefaction reactor located
immediately upstream of a heating zone and immediately downstream
of a torrefaction zone in relation to a biomass inlet of said
torrefaction reactor.
Torrefaction Time:
[0022] The time the temperature of the material is kept virtually
constant at the torrefaction temperature. The residence time of the
material in the torrefaction zone may be referred to as the
torrefaction time.
DETAILED DESCRIPTION
[0023] In a first aspect the invention relates to a torrefaction
method, comprising the steps of: [0024] a) subjecting an optionally
pretreated biomass to torrefaction to produce a torrefied material
and torrefaction gases; [0025] b) cooling and optionally
pelletizing the torrefied material from step a); [0026] c) mixing
at least part of the material from step b) with at least part of
the torrefaction gases and/or torrefied material from step a) such
that torrefaction gas components condense on the material from step
b).
[0027] In one embodiment step b) comprises transportation of the
torrefied material through a cooling device. Said cooling device
could be a drum and the transportation within said drum could be
mediated by means of a screw. In one embodiment the drum is cooled
by means for cooling wherein the means for cooling could be heat
exchangers. In another embodiment the screw is cooled. In a
preferred embodiment the cooling device is a screw cooler. In
another embodiment the cooling device comprises a water application
device for applying water to the torrefied material. In one
embodiment the temperature of the material from step b) is less
than 100.degree. C. The torrefied material which has been cooled
with the back-mixed (re-circulated) material may be transported
through the cooling device together with the backmixed material
such that torrefaction gas components can condense on the backmixed
material, particularly during the mixing but also in the cooling
device. In one embodiment torrefaction gases can also be sucked in
to the cooling device together with the torrefied material and cold
pellets. If torrefaction gases is sucked in to the cooling device
it may be preferred to direct the gases from the cooling device out
from the cooling device at a position upstream of an outlet for the
torrefied product so that gases having a relatively high content of
condensable components can be used for combustion. In other cases
it is important to get a product with high hydrophobicity and hence
the gases should be diverted from the cooling device later.
Therefore, according to one embodiment the cooling device comprise
a cooling device gas outlet upstream of an outlet for the torrefied
material. The gas outlet may for example be moveable along the
cooling device so that the position of the gas outlet can be
adjusted. According to another embodiment the torrefaction gases
are diverted out of the system for cooling a torrefied material
after the mixing zone but prior to the cooling device in order to
minimize clogging of the cooling device. In one embodiment the
temperature of the diverted gas is adjusted by controlling the
amount of cooled torrefied material supplied in the mixing zone. By
adjusting the temperature it is for example possible to save
organic acids in the gas while tar components condense on the
material.
[0028] There is a high demand for pellets of torrefied material on
the market. The inventors have however found that it is
particularly difficult to produce pellets of torrefied material
having a sufficient hydrophobicity. This is probably due to the
fact that the torrefied material is disintegrated (e.g. refined or
ground) in the pelletizing process, such that the hydrophobic
surface of the torrefied material is broken down and the interior
of individual pieces of torrefied material is exposed. But if the
pellets are mixed with torrefied material from the torrefaction
reactor such that torrefaction gases condense on the surfaces of
the pellets, the hydrophobicity of the whole pellets is increased.
Thus, in one embodiment the torrefied material is pelletized in
step b) and mixed with the torrefied material from step a) in step
c) and then separated from the torrefied material. The pelletized
material may for example be separated from the torrefied material
by means of a sieve, for example a sieve of mesh or by wind
sieving. That is, the separation may be based on size as the
pellets are normally smaller than the pieces of torrefied material,
in particular when they are derived from wood chips. The separation
may also be based on density.
[0029] In one embodiment the biomass is dried and optionally heated
prior to step a) to generate gases which are not mixed with the
torrefaction gases before or in step b). In this way, the humidity
of the torrefaction gases may be decreased such that they may be
combusted efficiently even though some of their organic material
have condensed on the back-mixed material.
[0030] In one embodiment the biomass is lignocellulosic biomass,
and in a preferred embodiment the biomass is a wood material, such
as wood chips.
[0031] Generally, the pellets mentioned in the present disclosure
can be replaced by other compacted materials such as briquettes.
Similarly the pelletizing mentioned in the present disclosure can
generally be replaced by other methods of compacting biomass or
solid fuels, such as briquette production. Another aspect of the
invention relates to a torrefaction system, comprising:
[0032] a torrefaction reactor for converting an optionally
pretreated biomass to a torrefied material and torrefaction
gases;
[0033] an arrangement comprising means for cooling and optionally
means for pelletizing the torrefied material, said arrangement
comprising an inlet connected to an outlet of the torrefaction
reactor;
[0034] a mixing zone for mixing the torrefaction gases and/or
torrefied material from the torrefaction reactor with material from
said arrangement such that torrefaction gas components may condense
on the material from said arrangement, wherein the mixing zone is
connected to an outlet of said arrangement via means for material
transport.
[0035] In one embodiment the mixing zone is arranged in the
connection between the outlet of the torrefaction reactor and the
inlet of the arrangement.
[0036] When the arrangement comprises means for pelletizing the
torrefied material, said system may for example further comprisea
device for separating pellets from torrefied material. In one
embodiment the separating device is arranged in the arrangement
upstream of the means for pelletizing the torrefied material. Also,
it may be arranged downstream of the means for cooling the
torrefied material. Thus, the back-mixed material and the torrefied
material from the torrefaction reactor may be transported through
the means for cooling together, In one embodiment the separating
device is a sieve or a mesh. In one embodiment the biomass is
lignocellulosic biomass and in a preferred embodiment the biomass
is wood such as wood chips.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0037] FIG. 1a shows a system for cooling a torrefied material (1),
comprising a torrefaction reactor (2) for converting biomass to a
torrefied material having a temperature of above 220.degree. C. and
torrefaction gases. In connection to an outlet of the torrefaction
reactor (2), a mixing zone (3) for mixing cold pellets of torrefied
material with hot torrefied biomass from the torrefaction reactor
is arranged. The torrefied material that has passed the mixing zone
(3) is fed together with the cold pellets into a cooling device (4)
for further cooling the torrefied material. Torrefaction gases can
also be sucked in to the mixing zone and/or into the cooling device
(4) together with the torrefied material and cold pellets.
Components of said torrefaction gases, as well as components of
gases given of from the torrefied biomass, will condensate on the
cooled pellets, which increases the hydrophobicity and energy yield
of the pellets and decreases condensation on the interior surfaces
of the cooling device (4), which thus reduces clogging of the
cooling device (4). The transport of the torrefied material in the
cooling device (4) is mediated by the rotation of a screw cooler.
The cooled torrefied material exits the cooling device (4) and
pellets are separated from the torrefied biomass in a separating
device (5) wherein the pellets exits the system for cooling a
torrefied material (1) through a first pellet outlet (8). The
cooled torrefied biomass is fed into a pelletizer (6) where it is
pelletized into pellets. At least part of these pellets are fed
back to the mixing zone (3), via means for pellets transport (7),
where the pellets are used to cool hot torrefied material from the
torrefaction reactor (2). Optionally, part of the pellets from the
pelletizer are not fed back to mixing zone. Instead, they may be
recovered from a second pellets outlet (9).
[0038] The skilled person understands that the pelletizer (6), the
separating device and the first pellets outlet (8) can be taken out
of the system such that, instead, one part of the cooled torrefied
material from the cooling device (4) is fed back via the means for
transport (7) and another part of the cooled torrefied material is
recovered through the pellets outlet (9).
[0039] FIG. 2a shows a torrefaction reactor having a biomass inlet
(21) wherein the biomass is introduced in the torrefaction reactor
by means of a feeding screw (22). The biomass is dried in a drying
zone (23)) wherein heat is supplied to the drying zone (23) by
means of a heating media (e.g. hot gases) through a drying zone
heating media inlet (24) and wherein the heating media leaves the
drying zone through the drying zone heating media outlet (25).
Dried biomass is transported through the drying zone (23) at a
speed regulated by the feeding speed in the biomass inlet (21) and
enters the heating zone (26) where the temperature of the biomass
is elevated to a temperature near the desired torrefaction
temperature. The heat is supplied to the heating zone (26) by means
of a heating media through a heating zone heating media inlet (27)
which leaves the heating zone through a heating zone heating media
outlet (28). The heated material enters a first torrefaction zone
(29) in which the temperature can be controlled by introducing
heating media and/or cooling media in the first torrefaction zone
heating/cooling media inlet (30) wherein said heating/cooling media
exits the first torrefaction zone through the torrefaction zone
heating/cooling media outlets (31). The biomass thereafter enters a
second torrefaction zone (32) heating/cooling media can be supplied
to the second torrefaction zone via the torrefaction zone cooling
media inlet (33) and said heating/cooling media exits the
torrefaction zone via a torrefaction zone cooling media outlet
(34). The material transport in the heating zone (26) and
torrefaction zones (29, 32) is driven by a common transport screw
which is attached to a drum enclosing the heating zone (26) and
torrefaction zones (29, 32).
[0040] FIG. 2b shows a torrefaction reactor having a biomass inlet
(21) wherein the biomass is introduced in the torrefaction reactor
by means of a feeding screw (22). The biomass is dried in a drying
zone (23) wherein heat is supplied to the drying zone (23) by means
of a heating media (e.g. hot gases) through a drying zone heating
media inlet (24) and wherein the heating media leaves the drying
zone through the drying zone heating media outlet (25). Dried
biomass is transported through the drying zone (23) at a speed
regulated by the feeding speed in the biomass inlet (21) and enter
the heating zone (26) where the temperature of the biomass is
elevated to a temperature near the desired torrefaction
temperature. The heat is supplied to the heating zone (26) by means
of a heating media through a heating zone heating media inlet (27)
which leaves the heating zone through a heating zone heating media
outlet (28). The transport of the biomass in the heating zone (26)
is mediated by a heating zone transport screw which is fixed to the
inner wall of a drum enclosing the heating zone (26). The material
transport in the heating zone is controlled by the rotational speed
of said drum and the biomass exits the heating zone through a
connecting zone and enters a first torrefaction zone (29) and
thereafter a second torrefaction zone (32). The temperature in the
torrefaction zone can be controlled by introducing heating media
and/or cooling media in the torrefaction zone heating/cooling media
inlets (30, 33) wherein said heating/cooling media exits the
torrefaction zone through the torrefaction zone heating/cooling
media outlets (31, 34). The biomass transport in the first
torrefaction zone (29) and second torrefaction zone (32) is driven
by a common transport screw which is attached to a drum enclosing
the first torrefaction zone (29) and second torrefaction zone (32).
The material transport in the torrefaction zones (29, 32) is
controlled by rotational speed of said drum can be rotated
independently of the drum enclosing the heating zone. Hence the
material transport in the torrefaction zone can be controlled
independently of the material transport in the heating zone.
[0041] FIGS. 3 and 4 show typical temperatures of the biomass in
the different zones in the torrefaction reactor disclosed in FIGS.
2a and 2b, wherein the torrefaction reactor is connected to the an
arrangement for cooling torrefied material as shown in FIG. 1. Zone
1 represents the drying zone (2), zone 2 represents the heating
zone (26), zone 3 represents the first torrefaction zone (29) and
zone 4 represents the second torrefaction zone (32). In the drying
zone (23) the biomass is dried, typically to a water content of
2-10% (w/w) and the temperature is elevated to about 100.degree. C.
In the heating zone (26), the temperature of the material is
elevated to close to the desired torrefaction temperature, which in
this example is 350.degree. C. In the torrefaction zones the
temperature is kept virtually constant at the desired torrefaction
temperature for a time corresponding to the desired torrefaction
time. The cooling zone represents the arrangement for cooling
torrefied material described in FIG. 1. The arrow indicates the
initial quench-cooling in the mixing zone (3) and thereafter the
torrefied material is cooled to a temperature below 100.degree. C.
in the cooling device (4) for further cooling the torrefied
material.
REFERENCES
[0042] [1] M. J Prins et al. More efficient biomass gasification
via torrefaction. Energy 2006, 31, (15), 3458-3470. [0043] [2] P.
C. A. Bergman et al. Torrefaction for Entrained Flow Gasification
of Biomass; Report C--05-067; Energy Research Centre of The
Netherlands (ECN): Petten, The Netherlands, July 2005; [0044] [3]
K. Hakansson et al. Torrefaction and gasification of hydrolysis
residue. 16th European biomass conference and exhibition, Valencia,
Spain. ETAFlorence, 2008. [0045] [4] A. Nordin, L. Pommer, I.
Olofsson, K. Hakansson, M. Nordwaeger, S. Wiklund Lindstrom, M.
Brostom, T. Lestander, H. Orberg, G. Kalen, Swedish Torrefaction
R&D program. First Annual Report 2009-12-18 (2009).
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